After being disappointed by an expensive docking system he grabbed a Jensen BT360 kit for about $35. It comes with an external speaker which would look horrid mounted on the dash. That speaker is meant to play your telephone audio via Bluetooth, while music from the phone is sent to the car stereo using an FM transmitter. Since he planned on hiding the control unit under the dash anyway, it wasn’t too hard to add some wires which intercept the audio being fed to that FM transmitter. From there he added a couple of relays to automatically route the audio signals (when present) and patched the whole thing into the Aux input. This way he doesn’t need the extra speaker, and all sound is feed to the head unit via wire instead of radio transmissions.

The final setup works pretty well. If a phone call comes in it automatically mutes the volume, or pauses the iPod if that’s what’s currently playing through the Aux port. [Aaron] thinks the bass from music played via Bluetooth is not quite as rich as when using the Aux port, but if you don’t mind the cables that’s still an option too.

Cool hack, but fair warning before you spend the money – the bass response on bluetooth is pretty bad compared to using a headphone jack, at least in my experience.

I have a kenwood excelon (their nice line) head unit with bluetooth, which I assumed would be as good as bluetooth could be. Its a 2010 model so the tech isn’t old.

I noticed bass response was not very good playing a song from my Android phone over the bluetooth. Playing the exact same song over the headphone jack produced nice punchy bass, but it was dull over bluetooth. I then played the same MP3 file using a USB stick plugged into the head unit and also got great bass response. I have noticed the same behavior after getting a newer Android phone.

My friend got a stereo with bluetooth in his car – also a nice unit, touchscreen and all that. I think his is an Alpine – either way its not Kenwood. He said bass response was great with his. I suggested he compare by playing the same song over the headphone jack and he came back and told me that I was right, and although he thought it was good quality, it was significantly worse than line in.

So moral of the story, if you care about audio quality and especially bass, bluetooth probably isn’t any good. Lots of you probably already know that, but I didn’t so I thought I’d share.

Out of curiosity, what kind of BT transmitter / receiver are you using? I’ve had the same experiences with bad quality as listed above previously myself. As you said, bitrate shouldn’t be an issue, and even if it was, you would loose the highs, not the lows. The higher the frequency, the higher the bandwidth needed to reproduce it ‘smoothly’. Bass should be an easy encode/decode, which makes me think the prefiltering before the ADC has an awfual response / is rolling bass out early, or the receiver is filtering out the bass with cheap or bad filtering after the DAC on it’s end… Thoughts? — It sure would be handy if this technology worked well… Maybe some caps could be pulled to drop a lowpass filter on the sender or receiver?

bluetooth transfer rate is actually not that much higher than that 700Kbps you cite. Bluetooth 2.1 is about 2.1Mbps maximum throughput. that could actually be an issue, especially if there’s interference.

Did I read this right? Using the phone over bluetooth via the stereo’s aux input and doing the music over FM?

Seems backwards to me since you’re so close to that aux input. Why not have a switcher/relay of some kind to get decent sound. I’m guessing music to phone call ratio is 80/20 music, at least for me it is.

I plug my phone in via aux the moment I get in the car and if I want hands-free then I just speak and they can hear me well, all sound is routed through the car speakers for both and there isn’t an echo/loop etc either.